4. Cerebellum And Brainstem, Schwannoma - Gross
Schwannomas are often called "acoustic neuromas" by clinicians
because, in the cranial vault, these neoplasms most often arise from
the acoustic, or 8th cranial, nerve. They are virtually always
benign. However, resection almost always results in deafness on that
side, because the acoustic nerve cannot be separated from the tumor.
Note the compression of the cerebral aqueduct and the necrosis of the
ipsilateral cerebellar hemisphere by the mass. There are two
categories of nerve sheath neoplasm: schwannoma and neurofibroma.
Most are benign. Patients with neurofibromatosis usually have
multiple tumors, sometimes in tremendous numbers. Nerve sheath tumors
in these patients are more likely to be malignant. A malignant nerve
sheath neoplasm is difficult to classify as either schwannoma or
neurofibroma and is usually called simply malignant nerve sheath
neoplasm.
